The present invention is directed to an improved laser optical element mounting arrangement and method. More particularly, the invention concerns an improved laser optical element mounting arrangement and method for mounting a laser optical element such as a reflecting mirror, a transmitting mirror, or an output window on its mounting element member of a laser.
The known laser optical element mounting arrangements typically involve the use of an O-ring or other sealant between the optical element and the adjacent support member and between cooperating support members in the vicinity of the optical element for sealing purposes, e.g., to prevent ingress of the atmosphere into the low pressure discharge cavity of a gas laser used in the earth's atmosphere or to prevent egress of the low pressure laser gases into the higher vacuum of outer space where the laser is used in outer space. Mechanical loading of the several parts of the optical element mounting arrangement is required to effectively seal the adjacent parts through the use of the O-ring or other sealant. The forces for this mechanical loading may not be uniformly distributed which can contribute to mechanical distortion of the optical element and resultant distortion of the laser beam. If the optical element is not uniformly and symmetrically cooled, thermal distortion can also occur. These known arrangements are also disadvantageous because the sealant materials can be degraded by scattered radiation from the laser output causing particles of the sealant material to contaminate the laser optical elements thereby reducing the performance of the laser. Further, when the optical elements are removed for cleaning and then remounted on the laser, retuning of the laser is normally required. Cleaning of the optical element can also degrade the sealing material. Degraded sealing material can migrate and get on the optical surfaces of the laser thereby deteriorating its performance. O-rings can also break down at the extremely high or low temperatures such as those encountered in outer space.
An object of the present invention is to provide an improved laser optical element mounting arrangement and method which avoid the aforementioned disadvantages of the known type of mounting arrangement and method. More specifically, an object of the invention is to provide a laser optical element mounting arrangement which permits the optical element to be removed for cleaning and then remounted on the laser with minimal or no laser retuning. An additional object of the invention is to provide a laser optical element mounting arrangement which enables uniform and symmetrical cooling of the optical element to prevent thermal distortion thereof. A further object of the invention is to provide a laser optical element mounting arrangement and method which do not mechanically distort the optical element. A still further object of the invention is to provide a laser optical element mounting arrangement and method which permit the elimination of a sealant material in the immediate vicinity of the optical element. Another object of the invention is to provide a laser optical element mounting arrangement having a vacuum seal which is not dependent on temperature stability to maintain the seal.
These and other objects of the invention are attained by a laser optical element mounting arrangement of the invention which comprises a laser optical element and a laser mounting support member. The mounting support member is provided with a mounting surface which is sufficiently smooth to form a vacuum seal with a surface of the optical element with which it is engaged. The vacuum seal can be broken and remade.
The method of mounting an optical element such as a reflecting mirror, a transmitting mirror, or an output window of a laser to a mounting support member thereof comprises the steps of providing an optical element mounting surface of a support member with a surface which is sufficiently smooth to form a vacuum seal with a surface of the optical element and engaging the surfaces to form a vacuum seal between the surfaces which can be broken and remade. The two surfaces which contact one another to form the vacuum seal may both be flat or both may be curved in a like manner for mating engagement. One surface could also be flat and the other curvilinear so that essentially line contact is formed to achieve the vacuum seal between the support member and optical element. According to the disclosed, preferred embodiment of the invention, only light, hand pressure contact of the engaging surfaces at ambient temperature is necessary to form a vacuum seal between the surfaces. No o-ring or other sealant is required.
The engaging surface of the optical element itself can be flat or curved, either concave or convex. It has a smoothness sufficient to form a vacuum seal with the surface of the support member. Where the surface is flat, it preferably has a flatness of about four or fewer fringes at 0.63 micron wavelength, and in the disclosed embodiment has a flatness of less than or equal to one fringe at 0.63 micron wavelength. Where the surface of the support member is flat it also preferably has a flatness of about four or fewer fringes at 0.63 micron wavelength.
The optical element is located within an opening of an additional support member which is releasably connected to the mounting support member. A resilient member is mounted between the additional support member and the optical element on the side of the optical element opposite the side of the optical element which is vacuum sealed to the mounting support member. In the disclosed embodiment, at least the surface of the optical element engaged with the mounting support member is coated with a layer material. The coating material can be metal, such copper, gold, a gold-silver alloy or silver. Such an outer metal coating can be located over a coating of nickel, for example, provided on at least the surface of the optical element which is adhered to the mounting support member. The coating material can also be a non-metallic material such as a non-metallic dielectric material. Alternatively, no coating need be applied on the optical element or at least not on the surface of the element which is vacuum sealed to the mounting support member.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, three embodiments in accordance with the invention.